Night panorama: how to fix vignetting

[Kostyanych]

I took a few shots today tonight. Then I tried to merge some pictures using Photoshop PhotoMerge.
And I saw a vignetting.
So the question is How can I get rid of vignetting?
Is it possible?

Have a look at my sample. I put the 2nd picture on the top of 1st and 3rd.

I did about 40-50% overlap for the next shoot, so you can see the brightness is different at the edge of the picture compared to the middle.


I shoot in manual mode (I left auto WB, just forgot about it).

Some tech specs: :)
20D
24-85 3.5-4.5 USM with EW-73II hood

Exif:

Camera
Make Canon
Model Canon EOS 20D
Image
Exposure time 13 s
F-number f/5
Exposure program Manual
ISO speed ratings 100
Aperture value f/5
Metering mode Pattern
Focal length 85 mm
Colorspace sRGB
Custom Rendered Normal process
Exposure mode Manual exposure
White balance Auto white balance
Scene capture type Standard
Canon Maker Notes
Macro mode Normal
Self timer 1e+001 s
Flash mode Flash not fired
Continuous drive mode Single
Focus mode One-Shot
Image size Large
Easy shooting mode Manual
Contrast High
Saturation High
Sharpness High
Metering mode Evaluative
Exposure mode Manual
White balance Auto
Flash Bias 0 EV
Image type Canon EOS 20D
Firmware version Firmware 1.1.0

[Jim_T]

It's your lens. The design is prone to vignetting. It would be much worse, if it weren't for the 1.6 crop due to the sensor size. There's a writeup on photo.net describing the problem

http://www.photo.net/bboard/q-and-a-fetch-msg?msg_id=003vP2

PS.. Vignetting is common to some extent in a lot of lenses..

[Tom W]

It appears that the 24-85 is a bit more prone to vignetting than other lenses, based on that discussion that Jim refers to. It shouldn't be as noticeable on the smaller sensor of the 20D, especially at longer focal lengths (that discussion is based on full-frame film cameras). But its apparently still there (or the exposure on the middle frame is slightly less - I'm on my laptop so I can't see things as well as I can at home).

There's a couple of things I can suggest. One, stop down more. Use f/8 and see what happens. Second, if you have a filter, get rid of it.

[Kostyanych]

Thanks a lot.
I will read the link carefully tonight.

I didn't use any filter and all settings were set up manually for all pictures (I didn't change any settings) ...

Well, I will have to try f/8 then. :)


... Just thinking.... Can we fix it with Photoshop? :)

[Jon]

Strictly, I don't think that's vignetting; more like cos^4 law of light fall-off (as you move away from the lens axis). One reason wide angle lenses almost invariably take pictures that gradually darken toward the edge. I'd recomend taking more pictures, with the lens zoomed to a longer focal length to minimize this. Also, use manual metering and don't use AWB, rather use one of the "constant" types.

[Kostyanych]

Thanks a lot.
I will try to play with it and we will see.